Abstract:

A device for clamping and unclamping of tools comprising a tool shaft, by
which device a sleeve section (2) of a tool holder (1) comprising a
centric receiver opening (4) for a shaft (5) of a rotation tool is
inductively heated, which sleeve section retains the shaft (5) of the
tool seated in the receiver opening (4) in a press fit, and releases it
upon heat up, which device comprises an induction coil assembly with at
least one induction coil (6), which can be fed by an electric current for
heating the sleeve section (2), and which comprises a concentrator body
(11), which is magnetically conductive and electrically nonconductive or
substantially electrically nonconductive, which concentrates the magnetic
flux of the induction coil (6) onto the portion of the tool side end of
the sleeve section (2), wherein the concentrator body (11) supports an
induction attachment (14) made of electrically conductive material.

Claims:

1-14. (canceled)

15. A device for clamping and unclamping of tools including a tool shaft
comprising:a tool holder having a sleeve section comprising a center
receiver opening for receiving the tool shaft, the sleeve section being
configured to be inductively heated, the sleeve section being configured
to retain the tool shaft seated in the receiver opening in a press fit
and being configured to release the tool shaft upon heating of the sleeve
section; andan induction coil assembly with at least one induction coil,
the induction coil assembly being configured to be fed by an electric
current for heating the sleeve section, the induction coil assembly
includes a concentrator body which is magnetically conductive and
electrically nonconductive or substantially electrically nonconductive,
wherein the concentrator body concentrates a magnetic flux of the at
least one induction coil onto a portion of a tool side end of the sleeve
section, and wherein the concentrator body supports an induction
attachment made of electrically conductive material.

16. A device according to claim 15, wherein:the induction attachment is
disposed relative to the concentrator body so that the concentrator body
is fluxed by a portion of a field extending outside of the concentrator
body so that a current is induced in the induction attachment; andthe
induction attachment is positioned and physically sized and configured so
that an opposite field is generated by the current induced therein, the
opposite field superimposing a magnetic field of the at least one
induction coil so that overall at least a local reduction of the magnetic
field of the at least one induction coil, which fluxes an exterior of the
device, occurs.

18. A device according to claim 15, wherein:the induction attachment is
made from copper.

19. A device according to claim 15, wherein:the induction attachment
comprises a folded over ring.

20. A device according to claim 17, wherein:a bottom face of the ring is
tilted upward relative to a top face of the sleeve section.

21. A device according to claim 20, wherein:the bottom face is tilted at
an angle of 10 to 14 degrees.

22. A device according to claim 15, wherein:a retaining ring surrounds the
concentrator body and simultaneously also maintains the induction
attachment in position relative to the concentrator body.

23. A device according to claim 22, wherein:the concentrator body and the
induction attachment are in direct surface contact with one another.

24. A device according to claim 23, wherein:the retaining ring is a
plastic ring formed by joint injection molding about the concentrator
body and about the induction attachment.

25. A device according to claim 24, wherein:the plastic of the retaining
ring partially or entirely reaches around the induction attachment, so
that plastic reduces a risk that a user is burned by the induction
attachment when the induction attachment is heated.

26. A device according to claim 15, further including:a yoke assembly made
of magnetizable, electrically nonconductive or substantially electrically
nonconductive material, wherein the yoke assembly in combination with the
sleeve section forms an at least partially closed magnetic loop about the
at least one induction coil; andan induction body made of electrically
conductive material associated with the at least partially closed
magnetic loop.

27. A device according to claim 26, wherein:the induction body is disposed
in a portion of a face of the at least one induction coil oriented
towards an end of the sleeve section.

28. A device according to claim 26, wherein:the induction body is
positioned and sized and shaped so that a current induced therein
generates an opposite field, which superimposes a magnetic field of the
coil, so that overall at least a local reduction of the magnetic field of
the coil is provided, which magnetic field fluxes an exterior of the
device.

29. A device according to claim 15, wherein:the induction body is made of
magnetically nonconductive material.

30. A device for clamping and unclamping of tools including a tool shaft
and a tool holder having a sleeve section comprising a center receiver
opening for receiving the tool shaft, the sleeve section being configured
to be inductively heated, the sleeve section being configured to retain
the tool shaft seated in the receiver opening in a press fit and being
configured to release the tool shaft upon heating of the sleeve section,
the device comprising:an induction coil assembly with at least one
induction coil, the induction coil assembly being configured to be fed by
an electric current for heating the sleeve section, the induction coil
assembly includes a concentrator body which is magnetically conductive
and electrically nonconductive or substantially electrically
nonconductive, wherein the concentrator body is for concentrating a
magnetic flux of the at least one induction coil onto a portion of a tool
side end of the sleeve section, and wherein the concentrator body
supports an induction attachment made of electrically conductive
material.

Description:

FIELD OF THE INVENTION

[0001]The invention relates to a device for inductive heating of the
sleeve section of a tool holder.

BACKGROUND OF THE INVENTION

[0002]In particular for tools rotating at high speed, like, e.g., cutters
or drills, it is known to shrink their shafts into a sleeve section of a
tool holder. The sleeve section is heated for this purpose by an
induction coil surrounding it, so that the tool shaft can be inserted
into the receiver opening of the sleeve section, which expands or
enlarges under heat influence. The outer diameter of the tool shaft is
slightly larger than the nominal diameter of the receiver opening, so
that the tool is held torque proof in the press fit of the tool holder
after the cooling of the sleeve section.

[0003]An inductive heating device suitable for this purpose is, e.g., the
heating device known from DE 101 02 710 A1. This device comprises an
induction coil, which can be placed over the sleeve section of the tool
holder, and which thus encloses the tool holder at a radial distance in
an annular manner, which induction coil is fed by AC power. The magnetic
field of the induction coil induces inductive currents in the
electrically conductive, mostly also magnetizable material of the tool
holder, which induction currents directly heat the sleeve section. The
induction coil extends axially at least over the engagement length, by
which the tool shaft reaches into the receiver opening and its winding
terminates in the portion of the tool side face of the sleeve section
axially with the sleeve section. In a radial direction, the inner
circumference of the induction coil extends at a distance from the sleeve
section in order to be able to use the same induction coil in tool
holders with a different outer diameter of the sleeve section.

[0004]At its face sides and at its outer circumference, the winding of the
induction coil is enveloped by a flux concentration assembly made of a
magnetizable (ferromagnetic or ferrimagnetic material), whose high
magnetic conductivity compared to air concentrates the magnetic flux
substantially to this envelope. The magnetizable material of the flux
concentrator assembly is electrically nonconductive in order to prevent
that the flux concentrator envelope heats also up inductively. The
portion of the flux concentration envelope adjacent to the tool side end
of the sleeve section is configured as a substantially annular
concentrator body, which directly contacts the tool side face of the
sleeve section in axial direction. It is the purpose of such a
concentrator body to induct the field into the sleeve section in a
controlled manner, in order to let it become effective therein and to
prevent at the same time that the tool shaft protruding from the sleeve
section is inductively heated by the scattered field portion, which would
also cause the tool shaft to expand, which is undesirable.
Advantageously, such a concentration body is provided as a shielding
collar, approximately as described in DE 101 02 710 A1. The shielding
collar captures a substantial portion of the field lines, which have
initially exited into the exterior space. Thus, it effectively prevents
that the outward protruding tool shaft gets heated up.

[0005]Nevertheless, even in such an assembly, a measurable scatter field
exists in the exterior of the induction coil or of the entire device.
However, this scatter field may not influence the primary function of
shrinking in and shrinking out in the major portion of the applications.

[0006]Recently, people not closely involved with the matter have become
more interested in electric "scatter fields".

SUMMARY OF THE INVENTION

[0007]It is an object of the invention to further reduce the field on the
outside of the inductive coil or on the outside of the device.

[0008]According to an aspect of the present invention, a concentrator body
indirectly or directly carries an induction attachment made of
electrically conductive and, preferably, magnetically nonconductive,
material. In this induction attachment, a magnetic field is generated,
which overlays the field of the induction coil extending in the exterior
of the induction coil or of the device, and thus partially weakening it.
This way, an active (typically additional) magnetic shielding is
accomplished, compared to the shielding which is accomplished by pole
shoes and similar items, which are made of materials which are
electrically nonconductive and magnetically conductive, like, e.g.,
ferrites, which can therefore be designated as "passive shielding".

[0009]According to another aspect of the present invention, the induction
attachment is fluxed by a portion of the field partially extending
outside of the concentrator body, so that a current is induced in the
induction attachment itself. Simply speaking, thus the field to be
reduced in the exterior of the coil automatically generates an opposite
field emanating from the induction attachment and weakening the first
field.

[0010]According to a further aspect of the present invention, the
induction attachment is typically provided as a ring, which is closed in
circumferential direction. This way, it assures an optimum shielding,
since the field lines of the high frequency field are then also really
captured in their entirety and they cannot escape the effect according to
the invention of the induction attachment.

[0011]An embodiment of the induction attachment can be made from copper.
Insofar, it has become apparent that in particular in the method
according to the invention, all other materials which appear equivalent
at first glance (like e.g. aluminum) develop a significantly inferior
effect.

[0012]According to another aspect of the present invention, the induction
attachment is configured so that it comprises the cross section of an
overlay ring. The induction attachment thus extends from the concentrator
body in radial direction beyond the concentrator and extends from the
concentrator body with a slight inclination (e.g., between 10° and
20° upward) relative to horizontal, when the concentrator body is
mounted as intended and aligned horizontally. This way, it forms a
substantial portion of the field lines, which otherwise have the tendency
to initially circumvent the concentrator body, which is a type of
obstacle which is effectively flowed by these field lines. The field
lines are thus used very effectively in order to generate Eddy currents
and thus generating a respective opposite field in the induction
attachment.

[0013]According to a further aspect of the present invention, the
concentrator body can be inserted in a retaining ring on its outside. The
retaining ring is used for positioning the concentrator body relative to
the magnetic coil assembly. Thus, the retaining ring simultaneously also
holds the induction attachment in position relative to the concentrator
body, (e.g., in a position in which the concentrator body and the
induction attachment are in direct surface contact with one another).
Thus, a substantial amount of heat from the induction attachment can
quickly flow into the concentrator body. Through such a configuration,
furthermore, the handling is also simplified, since the concentrator body
and the induction attachment fitting thereto are permanently connected
with one another, and can be jointly replaced by a respective unit made
of another concentrator body and another induction attachment fitting
thereto, without the user having to consider which induction attachment
has to be associated with which concentrator body. Furthermore, when the
concentrator body and the induction attachment are in direct surface
contact with one another, a very effective magnetic interaction between
the concentrator body and the induction attachment is assured, thus a
continuously shielded portion.

[0014]According to another aspect of the present invention, the retaining
ring can be configured as a plastic ring. A plastic ring is the simplest
means to take into consideration that there are relative movements
between the concentrator body and the induction attachment due to thermal
expansion, which is almost unavoidable, since the induction attachment,
different from the concentrator body, is heated up directly by the Eddy
currents generated therein.

[0015]The retaining ring, however, can also be configured as a ceramic
ring. This applies when the ceramic ring encloses the concentrator body
and the induction attachment with some clearance, so that the ceramic
ring cannot be broken through the thermal expansion of the induction
attachment or of the concentrator body. In view of this fact, retaining
rings made of ceramic, however, lead to manufacturing and tolerance
problems much more likely than the retaining rings made of plastic.

[0016]When the retaining ring is a plastic ring, the entire unit comprised
of the induction attachment, the concentrator body and the plastic ring
is ideally fabricated by inserting the concentrator body and the
induction attachment into a respective plastic injection molding machine
together, and molding plastic around it, which forms the retaining ring
after hardening.

[0017]The retaining ring can be made of a temperature resistant plastic,
which can maintain its shape at temperatures above 120° C., and up
to 150° C., so that its retaining function remains assured. The
production of the retaining ring from heat resistant plastic facilitates
that one or plural unshrinking cycles can be performed without a break in
between, and thus without the unit comprised of the induction attachment,
the concentrator body and the retaining ring failing, with at least the
induction attachment heating up enough, so that it thermally damages the
plastic of the retaining ring. PI- or PTFE plastics are particularly
suitable for the present application.

[0018]According to yet another aspect of the present invention, the
plastic of the retaining ring can completely or partially reach around
the induction attachment, and thus in particular also in the portion of
its outer circumference, which the user would certainly touch, when
attempting to lift the unit out of the induction attachment, and while
attempting to lift the concentrator body and the retaining ring out of
the device. This way, the risk is reduced that the user is burned
directly at the heated induction attachment, since the user touches the
highly heat conductive surface of the induction attachment directly.

[0019]The induction attachment can be provided or covered with an
interrupted plastic touch protection at least in some sections. The
interrupted touch protection is typically a component made of temperature
resistant plastic, e.g., a plastic as stated above or also Nylon®,
which is provided with a plurality of apertures, thus, which is
"interrupted". Through these apertures, cooling air (blown air or
convectively flowing air), or the coolant have direct access to the metal
surface of the induction attachment, whereby the induction attachment can
be effectively cooled in spite of the touch protection. Though tightly
spaced, each of the apertures is small enough compared to the bars
disposed between the apertures, so that the skin of the user, when
touching the induction attachment heated to 80° C. substantially,
does not directly contact the metal surface of the induction attachment
through the apertures and does not get burned due to the high heat
conductivity of the surface. Since it depends on the particular
application how large those apertures have to be and how tightly they
have to be spaced, many dimensions can be used. A person skilled in the
art can determine this for each actual application, considering that the
air or coolant access to the metal surface of the induction attachment
typically shall be restricted as little as possible, so that the metal
surface shall only be covered in as far as it is required for assuring
sufficient touch protection. The touch protection can either be provided
as an integral component of the retaining ring or as a separate
component. The interrupted touch protection can be provided as a type of
cage, which is closed at least in sections, which contacts the surface of
the induction attachment locally at the most, and whose "grid section" is
mostly offset from the surface of the induction attachment. The touch
protection can also contact the surface of the induction attachment
directly, e.g., like a net or like a grid.

[0020]The induction attachment can be configured, so that it has a large
heat capacity or mass, so that the end temperature of the induction ring
is less than 100° C., or less than 80° C., also after
plural shrink cycles, performed in direct sequence, in which a cold tool
holder is heated respectively, so that the associated tool can be
inserted and removed again. This is decisive, because a substantial
amount of heat is generated in the induction attachment through the
currents induced therein, which heat cannot be dissipated to the ambient
air in its entirety due to the shortness of time. Nevertheless, the
induction body must not heat up by an arbitrary amount. This is prevented
as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 shows an axial longitudinal sectional view through a device
according to the invention for inductively heating a tool holder with a
disk shaped pole shoe at the tool side end of the tool holder;

[0022]FIG. 2 shows an axial sectional view through the unit comprised of
the concentrator body, the induction attachment and the retaining ring;
and

[0023]FIG. 3 shows a semi-sectional view through a second alternative
embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0024]The illustrated embodiment includes a tool holder 1, which it is
made of a material which is at least electrically conductive, but also
magnetically conductive in this particular application, like, e.g.,
steel. At its other end, the tool holder comprises a sleeve section 2.
The sleeve section 2 includes a receiver opening 4, centrally disposed
relative to the rotation axis 3 of the tool holder, which receiver
opening 4 is configured to receive a rotating tool, e.g., a drill, a
cutter, or also a broaching tool, which is not shown in more detail,
which can be inserted into the receiver opening 4 with its shaft 5.

[0025]The outer diameter of the shaft 5 is slightly larger than the free
nominal diameter of the receiver opening 4, so that the shaft 5 is
supported in the sleeve section 2 in a press fit, whereby the necessary
torque can be transmitted to the rotation tool. In order to be able to
insert the tool shaft 5 into the tool holder 1, or in order to be able to
remove it from said tool holder, the sleeve section 2 is expanded by
heating. The heating is performed by means of an induction coil 6, which
is placed onto the sleeve section 2, and which concentrically envelopes
the sleeve section at a radial distance. The induction coil 6 is fed by
AC power or by pulsating DC power with a frequency of, e.g., 5 to 20 kHz.
The magnetic flux generated by a substantially cylindrical winding 7
induces Eddy currents in the sleeve section 2. The Eddy currents heat the
sleeve section 2 in a relatively short period of time, and thus
sufficiently expand the receiver opening 4 in order to be able to insert
the tool shaft or to pull it out.

[0026]The induction coil 6 has a coil body 8 made of temperature resistant
plastic or made of ceramics, onto which a multilayer winding 7 is
applied. The outer circumference and the face of the winding 7 pointing
away from the tool are covered with a one-piece- or multi-piece yoke
assembly made of a magnetically conductive- and electrically
nonconductive material, which focuses and concentrates the magnetic flux
onto the yoke assembly 9 in this surrounding portion of the winding 7.

[0027]The winding 7 provided with the yoke assembly 9 substantially
extends over the entire length of the receiver opening 4, or of the
sleeve section 2 configured for receiving the tool shaft 5.

[0028]In order to direct the magnetic flux from the yoke assembly 9, which
slightly protrudes beyond the winding 7 on this side in axial direction
to the face 10 of the sleeve section 2, in an optimum manner while
simultaneously shielding the portion of the tool shaft 5 which protrudes
beyond the sleeve section 2, and protecting from inductive heating, a
concentrator body 11 is associated with the face SF of the coil, which
concentrator body influences the field emanating from the yoke assembly
9. The concentrator body 11 can be configured in the form of a shielding
collar. It is also comprised of a magnetically conductive material, which
concentrates the magnetic flux, which material, however, is substantially
electrically nonconductive. This is the reason why it does not heat up
substantially under the influence of the magnetic field.

[0029]The concentrator body 11 thus configured extends on all sides at a
distance from the yoke assembly 9. The yoke assembly 9 does not extend
beyond the tool side face of the winding 7 in the illustrated embodiment,
but it only slightly protrudes beyond the face and it can also cover the
coil when required. The concentrator body has a flat contact surface 12
extending orthogonal to the axis and axially facing the sleeve section 2,
which contact surface contacts the annular face of the sleeve section 2
in a planar manner.

[0030]The concentrator body 11 is configured with a retaining ring 13 made
of a material which is also resistant against higher temperatures, and
which is magnetically and electrically nonconductive, which can be made
of plastic. By means of this retaining ring 13, the concentrator body 11
is fixated relative to the induction coil 6, however, so that it can be
exchanged with a concentrator body selected from a group of concentrator
bodies with slightly different shapes (not shown). The concentrator body
11 this way provides correct axial positioning of the respectively
inserted sleeve section 2 of the tool holder relative to the induction
coil 6. Furthermore, it can also be exchanged for adapting the same
induction coil 6 to the tool holder with different sleeve sections 2.

[0031]The annular gap remaining between the yoke assembly 9 and the
concentrator body 11 provided here in the shape of a shielding collar
increases the resistance in the magnetic loop of the induction coil 6. In
spite of that, the concentrator body 11, due to its configuration as a
shielding collar facilitates a concentration of the magnetic flux to the
sleeve section 2, which is substantially free from scatter fields in the
portion of the tool shaft 5. This way, the sleeve section 2 can be
inductively heated without causing excessive heating of the tool shaft 5.

[0032]According to an aspect of the illustrated invention, the
concentrator body 11 bears an induction attachment 14, its outside facing
away from the induction coil 6. Different from the concentrator body, the
induction attachment is comprised of an electrically well conductive
material, which, however, is magnetically nonconductive.

[0033]The induction attachment 14 is in direct large surface contact with
the concentrator body 11. The induction attachment 14 and the
concentrator body 11 touch one another substantially along the entire
upper planar surface of the concentrator body. This way, the induction
attachment 14 can very quickly transfer a portion of the thermal energy
generated in itself to the concentrator body 11 if necessary, which
prevents a possible overheating of the induction attachment 14.

[0034]The induction attachment 14 protrudes outward in radial direction
beyond the concentrator body 11. The induction attachment can extends
tilted upward, approximately at angle α of 10 to 20 degrees
relative to horizontal, as shown in FIGS. 1 and 2. The induction
attachment 14 can therefore be described as a circular ring with its
outer circumference folded over upward. This way, it forms a collar
extending outward beyond the concentrator body 11. The collar forms a
type of obstacle, which is fluxed through by a substantial portion of the
field lines, which otherwise tend to initially circumvent the
concentrator body 11 and tend to enter into the concentrator body 11
initially coming from a portion which is higher than the axis 3.

[0035]Therefore, Eddy currents are generated in the induction attachment
14, which Eddy currents naturally form a magnetic field by themselves, a
type of opposite field. Thus, the field to be weakened in the exterior of
the coil 9 automatically causes an opposite field with weakening effect
to emanate from the induction attachment 14.

[0036]The induction attachment is thus provided as a copper ring, closed
in circumferential direction. The induction attachment could also be
configured as an aluminum ring. However, it has become apparent that a
configuration as a copper ring provides a much more effective impact in
the current application or it leads to much lower heat up of the
induction attachment.

[0037]The concentrator body 11 and the induction attachment are disposed
in the common retaining ring 13, already briefly described above. The
retaining ring 13 is comprised of a highly temperature resistant plastic,
which is integrally injection molded with the concentrator body 11 and
the induction attachment 14. The plastic of the retaining ring 13 reaches
about the induction attachment 14 also in the portion of its largest
outer diameter, and thus prevents that the user comes into direct contact
at this location with the exposed hot- and naturally very heat conductive
surface of the induction attachment 14.

[0038]FIG. 3 shows a semi-sectional view through another embodiment of the
invention.

[0039]The embodiment of FIG. 3 differs from the embodiment described above
with reference to FIGS. 1 and 2 in that therein, the concentrator body 11
itself is not provided with an induction attachment, but that an
induction body 14a, which is also provided in a collar shape in this
application, is provided directly at the coil assembly 9, or at the coil
housing (in particular, in the portion of the face of the coil 6 oriented
towards the end of the sleeve section). Thus, the above statements apply
analogously as long as no physical features of the above induction
attachment are addressed, which are not shown in FIG. 3.

[0040]The functional principle of the induction body 14a is the same as
described above for the induction body described in the form of the
induction attachment 14. The induction body 14a is fluxed by the field of
the coil 6, which induces a current therein. The current generates an
opposite field, which partially weakens or directs the main field, so
that an active shielding occurs also here.

[0041]It is appreciated that a base section F, which supports a collar
shaped main section H of the induction body 14a, is preferably not
comprised of the same electrically conductive and magnetically
nonconductive material as the collar type main section H, but which is
preferably made of a plastic material. Thus, the thermal load on the
induction body is substantially reduced compared with the case where the
base section F is made of electrically conductive material.

[0042]Attaching or retaining the induction body independently from the
concentrator body has significant practical relevance, in particular for
systems with adjustable coils and/or adjustable concentrator bodies,
which do not have to be replaced, in order to reconfigure the system for
shrinking various sleeve diameters.

[0043]Furthermore, it is appreciated that active shielding elements with
comparable effect can also be mounted at the circumference of the coil,
e.g., in order to shield the actuation button of the coil.

[0044]In closing, it is appreciated that induction attachments as
described above certainly do not only work in conjunction with
concentrator bodies, configured as shielding collars.